Data storage technology focuses on providing the greatest capacity and availability, with the greatest performance, at a minimum cost. RAID technology increased the capacity of data storage systems for minimal cost by combining multiple independent, inexpensive hard disk drives into a large array. Later RAID technology increased data availability by adding fault tolerance at the expense of capacity and performance.
State of the art data storage systems are beginning to incorporate solid state drive (SSD) technology. SSDs are arrays of semiconductor memory elements, so every memory element is accessible with electrical signals as opposed to a hard disk drive which relies on mechanically spinning disks and mechanically actuated arms. SSDs are orders of magnitude faster than hard disk drives. SSDs are also more expensive than hard disk drives per unit of data storage.
Some data storage technologies have attempted to combine the performance of SSDs with the high capacity per unit cost of hard disk drives, but the high disparity in performance tends to negate the performance advantage of SSDs for any operation that accesses the hard disk drive.
Any data storage system attempting to incorporate multiple tiers of data storage devices to take advantage of the performance characteristics of each device will necessarily lose all of those performance advantages whenever the system performs an operation involving the slowest tier, such as a write operation. To provide data integrity, redundant fields are added, wasting capacity of faster, more expensive tiers, and slowing performance because of redundant write operations.
Consequently, it would be advantageous if a method and apparatus existed that are suitable for minimizing performance slowing operations and redundant capacity usage in a system having more than one storage tier, each storage tier having superior performance characteristics as compared to the previous tier.